Method of producing fuming nitric acid



April 29, 1952 Filed June 19, 1947' CON 0 EN SER GAS COOLING E w c& V M59 SI OE WV V E 3 GL 2 uv R RS.2 E E, H T m 5v L W A f? Wn E 5 L 2 ME R I 5 E 1 6 5V 0 RV D fi UwR my D Jdhn E. Rothr-ock ACID DISCHARGE FUMING AGENT Patented Apr. 29, 1952 UNITED STATES PATENT oFFIcE John E. Rothrock, Newark, Del., assignor to. Hercules Powder Company, Wilmington, .D. e l., a corporation of Delaware Application June 19, 1947,,Serial No.3 755,536

Ciaims. 1

Thislnvention relates to the manufacture of nitricacid and more particularly to a method of producingrfuming nitric acid having a highnitrogenoxidecontent.

Strong nitricacid may be made by concentration of weak nitric acid, the source of which is ammonia oxidation converter gases or other gases containing nitric oxides. Regardless of the source of nitrogen oxides, it has been the practice to feed the strong nitric acid vapor and N02 to a condenser from which it passes to an absorber. The vapors may be obtained from any type of nitric acid concentrator. Generally,'the condensate so obtained is in the order of 90-98% HNOs. While these processes have been adequate to produce strong nitric acid, they are incapable of producing fuming nitric acid having a high nitrogen oxide content. More specifically, when it is desired to produce fuming nitric acid, it has been the practice to install afuming nitric tower between the condenser'and the'absorber. Strong nitric acid in the order of 95 to 99% strength is circulated through the tower countercurrent to the gases from the condenser. This circulation is continued until the desired percentage of nitric oxides is shown to be present;

Now in accordance with this invention, it has been found that the fuming nitric tower may be eliminated entirely and, additionally important, it has been found that fumingnitric acid of high oxide content may be obtained directly. This latter feature is of extreme importancein the manufacture of products of specified oxide content. In the first place, it provides for obtaining an unusually high oxide contentyin the second place, it provides for flexibllity in operation to attain the greatest economies in blending the product produced to meet specifications as to oxide content.

Generally described, the present invention comprises passing a gas containing nitric acid vapor and oxides of nitrogen into a condenser in contact with the condensate of said gas to form oxide-enriched fuming nitric acid and withdrawing the oxide-enriched fuming nitric acid from thecondenser.

In practicing the invention, the gas containing nitric acid vapor and oxides of nitrogen is obtained from a'preceding operation either in the. gaseous or vapor phase or is preheated to render: it so. Temperatures slightly above the boiling point of the mixture have been found entirely adequate.

However, it has been found preferable to have thetemperature of the gas entering the system greaterthan 200 F. It has also been found that thepresence of a minor amount of liquid in the. gas entering the system is not detrimental.

The..:gas or. vapor is, fed into; ahhache her it bleaches the returning condensate from said ill vapor free ofoxides of, nitrogen. The gas then passes into a condenser, having. a plurality .of substantially horizontal sections arranged .-vertically to form ans-bend type condenser. The condenser is cooled from the top downward. Thus, the top section is the coolest and the-sections disposed thereunder are progressively-hotter. The condensate flows countercurrent. to the gas, that is, backward towardthe bleacher while the gas flows upward throughthe condenser.

In an intermediate portion of the condenser, there is provided means for withdrawing condensate of desired oxide content. The uncondensed acid and the unabsorbed gas-.from the upper, portion of the condenser are passed to an absorber in the conventional manner.

.Inoperation, the gas first condensed in the lower part of the condenser is nitricacidcontaming oxides of nitrogen. This acid flows to the bleacher and is mixed with the.hot incoming gases where the oxides of. nitrogen in the acid are boiled off and pass up the condenser again. Thus, the strong nitric acid obtained from the bleacher is substantially free of ,oxides of nitrogen and is of highstrength inthe order of -99%.

As the gas passes-into an intermediate portion of the progressively cooled condenser, the nitric acid condensate formed therein in contact with the gas reaches an equilibrium condition for maximum absorption of the oxides of nitrogen. It is in this region that thefuming. nitric acid of high oxide content is withdrawn. To accomplish this in a practical manner, samples of the condensate are taken at the varioussections and means for withdrawing the condensate from the section having the desired oxide content is provided. To insure a more flexible system relative-to variance incompos-ition of-feed gas,- itis preferred to install such means at more than one section for withdrawing the acid at desired oxide content.

A preferred embodiment of the invention' has been chosen for purposes of illustration-amidescription and is shown in the accompanying drawing.

Hot gas containing strong nitric acidand oxides of nitrogen is admitted through a-conduit |=intoa bleacher 3. 'Fromthe blea'chert; the gas passes into an S-bend condenser-5. "-The condenser 5 iscomposed of a plurality of tubular-sections I and 9 connected in reverseendtogend relationship. The sections 1 and-,9 .are arrangedin a verticalv zigzag pattern and ,the sections aresubstantially horizontal. The condensate formed in the condenser 5 flows ,along the bottom of the sections backwardly. toward thebleacher 3 and countercurrent to the flow t a T flo -pf; gas. is upwa d throug the condenser 5 into a conduit II which is connected to an absorption system (not shown). The flow of gas is maintained by suitable means such as a suction jet on the absorption system exhaust.

In an intermediate portion of the condenser 5, valved conduits I3 and I are provided to withdraw fuming nitric acid from the condenser. The valved conduits l3 and I5 are connected to a valved conduit H which discharges into a storage vessel I9. A valved conduit 2| is connected to the conduit I1 and valved conduits 23 and 25 connected to conduit 2| discharge into storage vessels 2'! and 29, respectively. A valved conduit 3| is provided from the bleacher 3 to the conduit 2|. Strong nitric acid substantially free of oxides of nitrogen from the bleacher may be discharged into the storage vessels by conduit 2| as desired. Valved conduits 33, 35 and 31 provide discharge of fuming nitric acid from the storage vessels [9, 21 and 29, respectively, through a valved discharge conduit 39. For cooling the condenser 5, a water spraying device 4? is disposed thereabove, The cooling water flows downwardly over the sections of the condenser.

An example of the operation of the invention is given. The operation was carried out in plant scale apparatus similar to that diagrammatically illustrated in the drawing.

Hot gas obtained from a Pauling Concentrating Tower was fed into the bleacher. This gas comprised 96.05% of HNOa and 1.70% of N02, by weight. The analysis of the gas was 93.72% free HN02, 1.70% N02, 0.76% 02, and 382% N2, by weight. Strong nitric acid was withdrawn from the bottom of the bleacher and fed to the storage vessels. This acid comprised 98.01% of HN03 and 0.04% of N02, by weight.

The gas from the bleacher passed into the S- bend condenser wherein a condensate was formed and the uncondensed and unabsorbed part of the gas passed to an absorption system. The reboiling of the N02 from the condensate formed fuming nitric acid having a high nitrogen oxide content within the condenser. The fuming nitric acid was withdrawn from an intermediate portion of the condenser and fed to the storage vessels. This acid comprised 102.85% of HNOa and 8.10% of N02, by weight. The analysis of the acid was 91.76% I-IN03, 8.10% N02, and 0.14% E20, by weight. The specific gravity of the acid was 1.556 at 60 F.

Operating data on the example run are as follows:

Gas fed to bleacher, 1500 lbs. per hour Strong nitric acid from bleacher, 1000 lbs. per

hour

Fuming nitric acid from condenser, 500 lbs. per

hour

Pressure on system, inch H20 Temperature of gas to bleacher, 222 F.

Temperature of gas from condenser. 80 F.

Temperature of strong nitric acid from bleacher,

Temperature of fuming nitric acid from condenser, 97 F.

In reference to the plant apparatus, the bleacher was approximately 2.3 feet in diameter and 4.5 feet high. A distributor was placed in the upper portion thereof to insure even distribution and contact of the downfiowing acid and the upflowing gas. The condenser was composed of eleven sections of pipe arranged in a vertical zigzag pattern. Each section was approximately six inches inside diameter and seven feet long. In this particular installation, the acid obtained from the fifth and the seventh section from the top was high in oxide content. The acid obtained from various runs analyzed 52-30% oxides as N02 by weight.

In the above example, the fuming nitric acid was obtained from the seventh section from the top and analyzed about 8% oxides as N02 by weight. The cooling water for the condenser was sprayed from a pipe extending substantially the length of the condenser sections. The three storage vessels had a capacity of 250 gallons each.

For materials of construction, aluminum and high silicon iron equipment were utilized and are preferred for the acid. However, stoneware and certain corrosion-resistant plastics may be used. In selection of materials of construction, it should be borne in mind that it is highly desirable that the system be designed and maintained to hold admission of atmospheric air into the system at a minimum, since it has been found preferable to operate the system under a slight subatmospheric pressure.

In carrying out the invention, it will be appreciated that oxides of nitrogen from sources other than that specifically mentioned in the example may be used. Fumes from operations involving oxidation or nitration with nitric acid and gases obtained by denitrating nitrocotton, and TNT spent acids may be used. Also, oxides of nitrogen from ammonia oxidation converters may be used. The prime requisite is that the feed gas going into the system must be predominantly in the gaseous or vapor phase.

In accordance with this invention, it will be appreciated that it is possible to obtain fuming nitric acid having an oxide percentage as high as 50% by weight. Fuming nitric acid having in the order of 30% free nitrogen oxide by weight has been readily obtained in the apparatus described above.

The product made in accordance with this invention is very corrosive and varies in color from light yellow to dark brown, depending on the content of dissolved oxides. It has a vapor pressure higher than normal 98100% nitric acid.

The principal uses of the product reside in fields where fuming nitric acid is generally used or where a powerful oxidizing'agent is desired.

The principal advantages of the present invention reside in the simplicity and flexibility of the process and the economy in initial installation, maintenance, and operation.

What I claim and desire to protect by Letters Patent is:

l. A method whereby concentrated clear nitric acid and fuming nitric acids of varying nitrogen oxide content can be simultaneously produced which comprises introducing into a bleacher a hot gaseous mixture comprising vaporous nitric acid and a substantial amount of gaseous oxides of nitrogen; passing the gas through the bleacher and upwardly into a condenser in countercurrent flow with the condensate of said gas to form oxide-enriched fuming nitric acid. in the condenser; and withdrawing an oxide-enriched fume ing nitric acid from an intermediate point in the condenser.

2. A method whereby concentrated clear nitric acid and fuming nitric acids of varying nitrogen oxide content can be simultaneously produced which comprises introducing into a bleacher a hot gaseous mixture comprising vaporous nitric acid and a substantial amount of gaseous oxides of nitrogen; passing the gas through the bleacher and upwardly into a condenser in countercurrent fiow with the condensate of said gas to form oxide-enriched fuming nitric acid in the condenser; withdrawing strong nitric acid substantially free of oxides of nitrogen from the bleacher; and withdrawing an oxide-enriched fuming nitric acid from an intermediate point in the condenser.

3. A method whereby concentrated clear nitric acid and fuming nitric acids of varying nitrogen oxide content can be simultaneously produced which comprises introducing into a bleacher a hot gaseous mixture comprising vaporous nitric acid and a substantial amount of gaseous oxides of nitrogen; passing the gas through the bleacher and upwardly into a condenser having a plurality of substantially horizontal levels and in countercurrent flow with the condensate of said gas to form oxide-enriched fuming nitric acid in the condenser; and, withdrawing an oxide-enriched fuming nitric acid from an intermediate point in the condenser.

4. A method whereby concentrated clear nitric acid and fuming nitric acids of varying nitrogen oxide content can be simultaneously produced which comprises introducing into a bleacher a hot gaseous mixture comprising vaporous nitric acid and a substantial amount of gaseous oxides of nitrogen; passing the gas through the bleacher and upwardly into a condenser having a plurality of vertically disposed substantially horizontal levels and in countercurrent flow with the condensate of said gas to form oxide-enriched fuming nitric acid in the condenser; and Withdrawing an oxide-enriched fuming nitric acid from at least one of the plurality of substantially horizontal levels in an intermediate portion of the condenser.

5. A method whereby concentrated clear nitric acid and fuming nitric acids of varying nitrogen oxide content can be simultaneously produced which comprises introducing into a bleacher a hot gaseous mixture comprising vaporous nitric acid and a substantial amount of gaseous oxides of nitrogen; passing the gas through the bleacher and upwardly into a condenser having a plurality of vertically disposed substantiall horizontal levels and in countercurrent flow with the condensate of said gas to form oxide-enriched fuming nitric acid in the' condenser; withdrawing strong nitric acid substantially free of oxides of nitrogen from the bleacher; and withdrawing an oxide-enriched fuming nitric acid from at least one of the plurality of substantially horizontal levels in an intermediate portion of the condenser.

6. A method whereby concentrated clear nitric acid and fuming nitric acids of varying nitrogen oxide content can be simultaneously produced which comprises introducing into a bleacher a hot gaseous mixture comprising vaporous nitric acid and a substantial amount of gaseous oxides of nitrogen; passing the gas through the bleacher and upwardly into a condenser having a plurality of vertically disposed substantially horizontal levels and in countercurrent flowwith the condensate of said gas to form oxide-enriched fuming nitric acid in the condenser; withdrawing strong nitric acid substantially free of oxides of nitrogen from the bleach-er; and withdrawin oxide-enriched fuming nitric acids of different oxide content from different substantially horizontal levels in an intermediate portion of the condenser.

7. A method whereby concentrated clear nitric acid and fuming nitric acids of varying nitrogen oxide content can be simultaneously produced which comprises introducing into a bleacher a hot gaseous mixture comprising vaporous nitric acid and a substantial amount of gaseous oxides of nitrogen, said gas being at a temperature greater than 200 F. at the point of entry into the bleacher; passing the gas through the bleacher and upwardly into a condenser having a plurality of vertically disposed substantially horizontal levels and in countercurrent flow with the condensate of said gas to form oxide-enriched fuming nitric acid in the condenser; withdrawing strong nitric acid substantially free of oxides of nitrogen from the bleacher; and withdrawing an oxide-enriched fuming nitric acid from at least one of the plurality of substantially horizontal levels in an intermediate portion of the condenser.

8. The method according to claim '7 in which the gas containing nitric acid and oxides of nitrogen is passed through the bleacher and into the condenser under subatmospheric pressure.

9. A method whereby concentrated clear nitric acid and fuming nitric acids of varying nitrogen oxide content can be simultaneously produced which comprises introducing into a bleacher a hot gaseous mixture comprising vaporous nitric acid and a substantial amount of gaseous oxides of nitrogen, said gas being at a temperature greater than 200 F. at the point of entry into the bleacher; passing the gas through the bleacher and upwardly into a condenser having a plurality of vertically disposed substantially horizontal levels and in countercurrent flow with the condensate of said gas to form oxide-enriched fuming nitric acid in the condenser; withdrawing strong nitric acid substantially free of oxides of nitrogen from the bleacher; and withdrawing oxide-enriched fuming nitri acids of different oxide content from difierent substantially horizontal levels in an intermediate portion of the condenser.

10. The method according to claim 9 in which the gas containing nitric acid and oxides of nitrogen is passed through the bleacher and into the condenser under subatmospheric pressure.

JOHN E. ROTHROCK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,197,167 Zeisberg Sept. 5, 1916 1,312,118 Hough Aug. 5, 1919 1,324,255 Jensen Dec. 9, 1919 1,590,043 Lentz June 22, 1926 1,695,619 Trautmann Dec. 18, 1928 1,832,853 Bennett Nov. 24, 1931 1,895,012 Spangler Jan. 24, 1933 1,939,162 Caro et al Dec. 12, 1933 2,403,902 Bell et a1. July 16, 1946 2,486,083 Watson Oct. 25, 1949 FOREIGN PATENTS Number Country Date 13,842 Great Britain Aug. 5, 1915 of 1914 131,642 Great Britain Sept. 4, 1919 685,531 Germany Dec. 21, 1939 OTHER REFERENCES Cottrell, Nitric Acid and Nitrates, vol. VI, page 342D, Van Nostrand and 00., N. Y. C., 1923.

Ephraim, Inorganic Chemistry, 4th ed., page 690, Nordeman Publishing 00., N. Y. C., 1943. 

1. A METHOD WHEREBY CONCENTRATED CLEAR NITRIC ACID AND FUMING NITRIC ACIDS OF VARYING NITROGEN OXIDE CONTENT CAN BE SIMULTANEOUSLY PRODUCED WHICH COMPRISES INTRODUCING INTO A BLEACHER A HOT GASEOUS MIXTURE COMPRISING VAPOROUS NITRIC ACID AND A SUBSTANTIAL AMOUNT OF GASEOUS OXIDES OF NITROGEN; PASSING THE GAS THROUGH THE BLEACHER AND UPWARDLY INTO A CONDENSER IN COUNTERCURRENT FLOW WITH THE CONDENSATE OF SAID GAS TO FORM OXIDE-ENRICHED FUMING NITRIC ACID IN THE CONDENSER; AND WITHDRAWING AN OXIDE-ENRICHED FUMING NITRIC ACID FROM AN INTERMEDIATE POINT IN THE CONDENSER. 